1. Field of the Invention
The present invention relates generally to a cathode-ray tube (CRT) apparatus, and more particularly to a CRT apparatus having an electron gun assembly capable of effecting dynamic astigmatism compensation.
2. Description of the Related Art
In general terms, a color CRT apparatus comprises an in-line electron gun assembly that emits three electron beams, and a deflection yoke that produces deflection magnetic fields for deflecting the three electron beams emitted from the electron gun assembly and causing them to horizontally and vertically scan the phosphor screen. The deflection yoke produces non-uniform magnetic fields comprising a pincushion-shaped horizontal deflection magnetic field 74, as shown in FIG. 11, and a barrel-shaped vertical deflection magnetic field.
An electron beam 63 (B, G, R) that has passed through the non-uniform magnetic fields suffers a deflection aberration, i.e. astigmatism due to the deflection magnetic fields. Specifically, the electron beam 63 traveling to a peripheral portion of the phosphor screen suffers a force as indicated by arrows a and b by the deflection magnetic field 74. Consequently, as shown in FIG. 12, the beam spot on the peripheral portion of the phosphor screen deforms to have a vertically elongated low-luminance halo portion 76 and a horizontally elongated high-luminance core portion 75. Such deformation of the beam spot occurs at peripheral portions of the screen in the vertical direction V, horizontal direction H and diagonal direction D, as shown in FIG. 13. The deformation considerably degrades the resolution.
In order to improve the degradation in resolution, an electron gun assembly has been proposed, for example, in Jpn. Pat. Appln. KOKAI Publication No. 3-93135 and Jpn. Pat. Appln. KOKAI Publication No. 3-95835. In the proposed electron gun assembly, as shown in FIG. 14, a fourth grid G4 and a sixth grid G6 are supplied with a dynamic focus voltage obtained by superimposing an AC component E4 varying in synchronism with the deflection magnetic fields upon a DC voltage E3. Thereby, a first quadrupole lens is created between the third G3 and fourth grid G4, and a second quadrupole lens is created between the fifth grid G5 and sixth grid G6.
In this electron gun assembly, the first quadrupole lens corrects image-magnifications which differ in horizontal and vertical directions. At the same time, the second quadrupole lens and an ultimate focusing lens, which is created between the sixth grid G6 and seventh grid G7, function to prevent the electron beam 63, which is ultimately deflected onto the peripheral portion of the screen, from being extremely deformed by the deflection aberration due to the deflection magnetic fields.
With the deflection of the electron beams, potential differences vary between the fourth grid G4 and sixth grid G6 supplied with the dynamic focus voltage, on the one hand, and the adjacent third grid G3, fifth grid G5 and seventh grid G7, on the other. Accordingly, the coulomb force varies between the grids G3 through G7. Owing to the variation in coulomb force, mechanical vibrations occur in the grids G3 through G7. The mechanical vibrations are transmitted to the funnel via insulating supports, which support the grids G3 to G7, and stem pins electrically connected to the grids G3 to G7. Consequently, the funnel vibrates, and abnormal noise is produced from the funnel.
The third grid G3 is a main factor that increases the amplitude of vibration of the funnel. The first reason is that the distance between the third grid G3 and fourth grid G4 is narrower than that between the third grid G3 and second grid G2. Thus, the variation in coulomb force between the third grid G3 and fourth grid G4 is greater than that between the second grid G2 and third grid G3, and vibration easily occurs between the third grid G3 and fourth grid G4. The second reason is that the third grid G3 is formed of a plate-shaped electrode. Therefore, compared to a cup-shaped electrode body such as the fifth grid G5 that extends in the tube-axis direction, the third grid G3 has a lower flexure rigidity to vibration in the tube-axis direction and tends to vibrate easily.
More specifically, the third grid G3 is a plate-shaped electrode and is supported and fixed by insulating supports at its upper and lower portions. The coulomb force acting between the electrodes is mainly applied to an intermediate portion between the two support points at the upper and lower portions of the third grid G3 when the third grid G3 is supported at these two points. Consequently, as shown in FIG. 16, the third grid G3 flexes in the tube-axis direction and vibrates.
The vibration occurring at the third grid G3 and fourth grid G4 is modulated while being transmitted to the funnel. The vibration is frequency-modulated or increased by a resonance phenomenon due to the frequency of the dynamic focus voltage and the natural vibration characteristics of the third grid G3 and fourth grid G4 in the tube-axis direction. Consequently, the funnel vibrates at audio frequencies (20 Hz to 20 kHz) and produces abnormal noise. The natural vibration characteristics, that is, the characteristic frequency, are determined by the distance between the paired insulating supports that fix the electrode, the thickness of the electrode, the hardness of the electrode material, the electrode structure, etc.
In particular, when such a high-frequency voltage as to vary in synchronism with the horizontal deflection magnetic field is applied as the dynamic focus electrode, abnormal noise at a higher level may be produced due to resonance. Moreover, it has been made clear by experiments that the abnormal noise increases as the fourth grid G4 and sixth grid G6 supplied with the dynamic focus voltage are disposed closer to the cathodes K (on the stem section side) accommodating heaters.
The reasons appear to be that (1) the stem pins are firmly fixed to the stem section by means of welding, and so vibration occurring in each grid may easily be transmitted, (2) the electrode supplied with the dynamic focus voltage is formed of a plate-shaped electrode, and so it may easily transmit the vibration, and (3) the electrode supplied with the dynamic focus voltage is disposed near the heaters, and thus it may easily thermally expand. It is assumed that these factors may be combined in a complex fashion and a large abnormal noise is produced.
A dynamic focus voltage including an AC component E4 of 40 kHz to 100 kHz was applied to the fourth grid G4 and sixth grid G6 of the CRT apparatus with the electron gun assembly 64 shown in FIG. 14. The level of produced abnormal noise was measured. FIG. 15 shows the measured results.
In FIG. 15, the abscissa indicates the frequency of the AC component E4 included in the dynamic focus voltage, and the ordinate indicates the level of sound pressure sensed by humans in 10 grades. Normally, the level of abnormal noise needs to be suppressed to level 2 or less, at which the noise is hardly sensed by humans or negligible as being not unpleasant. According to the measured results shown in FIG. 15, the noise level exceeds level 2 at many frequency bands. If abnormal noise of level 2 or more has occurred, even if good image characteristics are obtained by the application of the dynamic focus voltage, the viewer feels unpleasant, and the product value and reliability of the CRT apparatus are greatly degraded.
The present invention has been made in consideration of the above problems, and its object is to provide a cathode-ray tube apparatus which can suppress abnormal noise and has a high product value and reliability.
According to an aspect of the invention, there is provided a cathode-ray tube apparatus comprising: a substantially rectangular face panel; a funnel made continuous with the face panel; a phosphor screen formed on an inner surface of the face panel; an electron gun assembly disposed within a neck of the funnel and including an electron beam generating section that generates electron beams, and a main lens section that focuses the electron beams on the phosphor screen, the electron gun assembly having a plurality of electrodes including a dynamic focus electrode to be supplied with a dynamic focus voltage; a deflection yoke which produces deflection magnetic fields that horizontally and vertically deflect the electron beams emitted from the electron gun assembly; an insulating support which extends in a tube-axis direction and supports and fixes the plurality of electrodes of the electron gun assembly; and a plurality of stem pins provided at one end of the neck and electrically connected to the electrodes of the electron gun assembly, wherein the dynamic focus voltage is a voltage obtained by superimposing an AC component varying in synchronism with the deflection magnetic fields upon a reference voltage, the dynamic focus electrode comprises embedment portions to be embedded in the insulating support, electron beam passage holes that pass the electron beams through, and a vibration-damping portion formed in the surface including the electron beam passage holes to suppress vibration in the tube-axis direction, and the vibration-damping portion is formed of a recessed/projected portion recessed or projected in the tube-axis direction.
According to another aspect of the invention, there is provided a cathode-ray tube apparatus comprising: a substantially rectangular face panel; a funnel made continuous with the face panel; a phosphor screen formed on an inner surface of the face panel; an electron gun assembly disposed within a neck of the funnel and including an electron beam generating section that generates electron beams, and a main lens section that focuses the electron beams on the phosphor screen, the electron gun assembly having a plurality of electrodes including a dynamic focus electrode to be supplied with a dynamic focus voltage; a deflection yoke which produces deflection magnetic fields that horizontally and vertically deflect the electron beams emitted from the electron gun assembly; an insulating support which extends in a tube-axis direction and supports and fixes the plurality of electrodes of the electron gun assembly; and a plurality of stem pins provided at one end of the neck and electrically connected to the electrodes of the electron gun assembly, wherein the dynamic focus voltage is a voltage obtained by superimposing an AC component varying in synchronism with the deflection magnetic fields upon a reference voltage, at least one of the electrodes, which is adjacent to the dynamic focus electrode, comprises embedment portions to be embedded in the insulating support, electron beam passage holes that pass the electron beams through, and a vibration-damping portion formed in the surface including the electron beam passage holes to suppress vibration in the tube-axis direction, and the vibration-damping portion is formed of a recessed/projected portion recessed or projected in the tube-axis direction.
According to another aspect of the invention, there is provided a cathode-ray tube apparatus comprising: a substantially rectangular face panel; a funnel made continuous with the face panel; a phosphor screen formed on an inner surface of the face panel; an electron gun assembly disposed within a neck of the funnel and including an electron beam generating section that generates electron beams, and a main lens section that focuses the electron beams on the phosphor screen, the electron gun assembly having a plurality of electrodes including a dynamic focus electrode to be supplied with a dynamic focus voltage; a deflection yoke which produces deflection magnetic fields that horizontally and vertically deflect the electron beams emitted from the electron gun assembly; an insulating support which extends in a tube-axis direction and supports and fixes the plurality of electrodes of the electron gun assembly; and a plurality of stem pins provided at one end of the neck and electrically connected to the electrodes of the electron gun assembly, wherein the dynamic focus voltage is a voltage obtained by superimposing an AC component varying in synchronism with the deflection magnetic fields upon a reference voltage, each of the dynamic focus electrode and at least one of the electrodes, which is adjacent to the dynamic focus electrode, comprises embedment portions to be embedded in the insulating support, electron beam passage holes that pass the electron beams through, and a vibration-damping portion formed in the surface including the electron beam passage holes to suppress vibration in the tube-axis direction, and the vibration-damping portion is formed of a recessed/projected portion recessed or projected in the tube-axis direction.
According to the cathode-ray tube apparatus, each of the dynamic focus electrode and at least one of the electrodes, which is adjacent to the dynamic focus electrode, comprises embedment portions. Thereby, a flexure phenomenon due to vibration in the tube-axis direction can be suppressed. Specifically, when a dynamic focus voltage is applied, a coulomb force acting between the dynamic focus electrode and the adjacent electrode varies in synchronism with the frequency of the AC component included in the dynamic focus voltage. This results in a tube-axis-directional mechanical vibration of each electrode and a flexure vibration of the electrodes. However, these vibrations can be suppressed.
As is shown in FIG. 17, the plate-shaped dynamic focus electrode (G3-1) has the recessed/projected vibration-damping portion (X3) in the surface including the electron beam passage hole (X2). When the vibration-damping portion is not provided, the coulomb force acts mainly at an intermediate portion, i.e. the electron beam passage hole, between the upper and lower support fixture points. By contrast, with the vibration-damping portion provided, the coulomb force acts mainly at the recessed/projected vibration-damping portion. At the same time, the coulomb force acting on the whole electrode is dispersed by the vibration-damping portion, and a flexure phenomenon does not easily occur.
Thereby, a resonance phenomenon due to the frequency component in the AC component and the natural vibration characteristics of the electrode can be suppressed. Accordingly, the frequency modulation of mechanical vibration caused by the electrode due to coulomb force variations and the increase in the tube-axis-directional vibration amplitude can be suppressed. Therefore, the occurrence of mechanical vibration transmitted to the funnel via the insulating support and stem pins can be reduced, and the occurrence of abnormal noise suppressed. Thus, a CRT apparatus with high product values and reliability can be provided.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.